We have found that Sertoli cell secretory protein S70 share antigenic homology with polypeptide components of Sertoli cell secretory protein S45-S35 heterodimeric protein. We have made the unexpected observations that polyclonal antisera raised against these two Sertoli cell secretory proteins crossreact with outer dense fiber polypeptides of sperm tail and that a polyclonal antiserum generated against a major polypeptide of outer dense fibers of sperm tail crossreacts with protein S70 and its breakdown products. These findings suggest a possible product-precursor relationship between S70 and S45-S35 heterodimeric protein and raise important questions concerning the cell origin and molecular organization of outer dense fiber polypeptides of the sperm tail. To determine whether S70 is a precursor for S45-S35 heterodimeric protein, we will analyze the structure and expression of S70 and S45-S35 heterodimeric protein genes and search for regions of genomic homology in spermatogenic cells. Polyclonal antibodies raised against these two Sertoli cell secretory proteins will be used to screen rat testis cDNA expression libraries in lambda gtll phage expression vector. Inserts from positive clones will be subcloned into a multifunctional plasmid vector to determine the complete cDNA sequence and derive protein amino acid sequence. Derived amino acid sequence will be compared with N- terminus amino acid sequence analysis of protein S70 and outer dense fiber polypeptides. cDNA will be used for in situ cytohybridization and Northern blot experiments to determine whether spermatogenic cells, mainly spermatids, contain genome sequences and transcripts complementary to Sertoli cell secretory proteins. To determine whether Sertoli cell secretory proteins are related to outer dense fiber polypeptides, we will raise polyclonal antibodies against purified outer dense fiber polypeptides from sperm tail and search for crossreactive epitopes and N-terminus amino acid sequence homology of Sertoli cell secretory protein S70 and S45-S35 heterodimeric protein and outer dense fiber polypeptides. The subcellular localization and fate of both Sertoli cell secretory proteins and outer dense fiber polypeptides will be determined in rat testis by immunogold electron microscopy. Ultimately, the ontogeny, hormonal and spermatogenic cell dependency of Sertoli cell secretory proteins S70 and S45-S35 heterodimeric protein gene activity and expression will be determined in rat testis during development and in cultured Sertoli cells using an automated cell perifusion system combined with radioimmunoassay.